PALEOZOIC MAGMATIC ACIDID ROCKS PRESERVED IN THE BASEMENT OF THE SIERRA MADRE ORIENTAL, CIUDAD VICTORIA, TAMAULIPAS: EVOLUTION OF ORDOVICIAN AND CARBONIFEROUS ARCS ALONG THE NW-MARGIN OF GONDWANA

The eroded core of the Huizachal–Peregrina Anticlinorium is a major structure of the Mexican Sierra Madre Oriental located west of Ciudad Victoria, Tamaulipas. Its eroded core offers a unique geological window to the Precambrian and Paleozoic units that together comprise its basement. Among them two felsic, unmetamorphosed magmatic units are present: a) the Ordovician Peregrina Tonalite, emplaced into the Neoproterozoic Novillo Metamorphic Complex and in tectonic contact to the Carboniferous Granjeno Schist, and b) the Carboniferous Aserradero Rhyolite, interbedded in the Paleozoic Tamatán sedimentary sequence. A cogenetic relationship between both units have been ruled out, because of the quite different ages and contrasting geochemical compositions. Peregrina Tonalite represents the northern most expression of the Peregrina – Mochonian Orogen, which is considered as an extension of the Southamerican Famatinian arc into Mexico. In contrast Aserradero Rhyolite has been very poorly described and remained until now as an exotic lithodeme wedged discordantly between the siliciclastic Carboniferous formations of the Tamatán Basin. The correlation to other coeval rhyolitic and granitic units from Mexico and its meaning to the Tamatán Basin development itself has been not yet revised. The goal of this study is to understand the evolution of two arcs that led to the generation of acidic rock in different times, using geochemical data and U–Pb zircon crystallisation ages. The products of these arcs are well preserved in the Sierra Madre Oriental basement represent important vestiges of successive pre-Andean subduction stages along the NW border of Gondwana, without the involvement of the accretion of exotic terranes.